A DNS, or domain name system, server error occurs when the client, or Web browser, cannot communicate with the DNS server either because there is an issue with DNS routing to the domain or the server is down. The DNS server is responsible for converting the website URL, or uniform resource locator, into an IP address that is required for actual communication. DNS errors are the most common errors received by users while browsing the Web.
The most common problem linked to DNS errors is network failure. Network failures typically occur when a server in the network does not relay information properly to the next server, or when the network settings are not properly configured. The quickest way to troubleshoot a network problem is to confirm the network connectivity by pinging other routers or computers that are on the same network as the DNS servers.
A DNS error can also occur if the security software or firewall has blocked the computer from communicating with certain websites. Viruses are also common causes of DNS errors. A virus may integrate itself into the TCP/IP stack and intercept name resolution requests.
The best way to troubleshoot a DNS error is by using the NSLOOKUP command, which is accessed from the Windows Command Prompt Window.